1. Field of the Invention
The present invention relates to an optical system and a projection type image display apparatus configured to guide light emitted from a lamp source to an image display region of a reflection type display device along a predetermined optical path, to reflect a light component which forms an image to be projected by the image display region, and to project the reflected light component onto a predetermined screen.
2. Description of the Background Art
A conventional reflection type image display apparatus is known in which light emitted from a lamp source is guided to an image display region of a reflection type display device along a predetermined optical path, and a light component which forms an image to be projected is reflected by the image display region, and the reflected light component is projected onto a predetermined screen (e.g., Japanese Patent Application Laid-Open No. 2000-98272 and 2001-183603).
In this type of apparatus, light emitted from a light source is converted into light having a substantially uniform illumination distribution by a rod lens or the like, and the converted light is guided to the reflection type display device, and light which forms an image reflected by the image display region of the reflection type display device is projected onto the screen.
In such projection type image display apparatus, a light outgoing surface of an optical member such as a rod lens for converting light into the state that illumination distribution is substantially uniform generally has a conjugate relationship with an image display region of a reflection type display device. Thus, the light outgoing surface of the optical member and the image display region of the reflection type display device are formed in a substantially similar shape.
Further, since an image reflected by the reflection type display device is scaled up or down to be projected onto the screen, the image display region of the reflection type display device and the projected image on the screen are in a similar shape.
Therefore, when an image having an aspect ratio (the ratio between the width and height of an image) of 4:3 is to be projected, the light outgoing surface of the optical member, the image display region of the reflection type display device and the screen size are all configured to have an aspect ratio of 4:3.
In the case that an image having an aspect ratio of 16:9 is projected with such apparatus, the optical member transmits light for irradiating the whole area of the image display region of the reflection type display device while the reflection type display device is controlled so as to perform image formation only in the central portion of the image display region and to prevent light entering the other portion from being reflected toward the screen.
In this case, however, part of light is also reflected by a portion other than the central portion of the image display region, and the reflected light is projected onto the screen. This causes a problem in that, although top and bottom regions of a image projection region on the screen where images are inherently unnecessary to be displayed need to be displayed in black, a part or the whole of the top and bottom regions is displayed brightly, that is, displayed in white (hereinafter referred to as a “whitening phenomenon”). Such whitened region appears in the vicinity of a projected image, causing another problem in that, particularly in the application to a video projector and in viewing video in a dimly lit room in order to enhance a realistic sensation of video, such region interferes with viewing and reduces the realistic sensation. Also, in the application to a data projector used for presentation or the like, viewers cannot concentrate on a projected image, causing the effect of presentation to be degraded.
Further, light outgoing from the light outgoing surface of the optical member is irradiated onto the whole area of the image display region of the reflection type display device, which means light incident upon a portion other than the central portion of the image display region is not utilized effectively. This disadvantageously causes images projected onto the screen to be darkened.
Due to these factors, a conventional projection type image display apparatus cannot display images having an aspect ratio of 16:9 in good condition.